1. Field of the Invention
The present invention relates to an organic EL display and a method of manufacturing the same.
2. Description of Related Art
FIG. 1 is a cross-sectional view illustrating a conventional organic EL display, and particularly shows a low molecular organic EL display.
The organic EL display of FIG. 1 includes an anode electrode 12, a hole injection layer 13, a hole transport layer 14, an organic light-emitting layer 15, an electron transport layer 16, an electron injection layer 17, and a cathode electrode 18, which are stacked on a substrate 11 in described order. Of the layers, the electron transport layer 16 can be removed.
Eventhough not shown, a high molecular organic EL display generally includes an anode electrode, a hole transport layer, an organic light-emitting layer, and a cathode electrode, which are sequentially stacked.
Holes move from the anode electrode 12 to the organic light-emitting layer 15, and electrons move from the cathode electrode 18 to the organic light-emitting layer 15. The organic light-emitting layer 15 emits light by excitation and recombination of electrons and holes injected from a cathode and an anode. Therefore, if the hole injection efficiency and the electron injection efficiency are improved, the device characteristics of the organic EL display are also improved.
In the case of a low molecular organic EL display, the layers are formed using a vacuum deposition technique. However, in case of a high molecular organic EL display, the layers are formed using a solution processing technique, which result in certain limitations to forming the organic light-emitting layer made of an organic material.
In particular, the hole transport layer must be stable to a wet coating process to form the organic light-emitting layer using an organic solvent. The hole transport layer is generally made of a water-soluble high molecular material such as a PEDOT (a mixture of a poly(3,4)-ethylenedioxythiophene and a polystyrenesulfonate) or a PANI (a mixture of a polyaniline and a polystyrenesulfonate). However, such a hole transport layer has a problem in that an interface characteristic between the hole transport layer and the hydrophobic organic light-emitting layer is lowered.
For example, since a bonding power between the hole transport layer and the organic light-emitting layer is low, a life span of the organic EL display is shortened. Also, uniform organic light-emitting layer cannot be formed on the hydrophilic hole transport layer using an ink-jet printing technique or a laser induced thermal imaging (LITI) technique, even though the ink-jet printing technique and the LITI technique have an advantage in that it is easy to define pixels and achieve a full color light emission.
Another problem for the organic EL display is there is a poor interface characteristic between an anode electrode and a hole transport layer. Migration of oxygen from the anode electrode to a hole transport layer or a light-emitting layer and permeation of moisture through the anode/hole transport layer or the hole transport layer/light-emitting layer interface can damage the device characteristic of the organic EL display.
In efforts to overcome the problems described above, a silicon oxide layer or a silicon nitride layer is arranged between the anode electrode and the hole transport layer so as to improve a device characteristic of the organic EL display.
U.S. Pat. No. 4,954,528 discloses a silicon carbide (SiC) layer arranged between the anode electrode and the hole transport layer. U.S. Pat. No. 4,188,565 discloses a silicon oxynitride layer arranged between the anode electrode and the hole transport layer. U.S. Pat. No. 5,643,685 discloses a silicon oxide layer arranged between the anode electrode and the hole transport layer. U.S. Pat. No. 5,476,725 discloses a tantalum oxide layer arranged between the anode electrode and the hole transport layer. However, the U.S. patents stated above require a high vacuum process and have a complicated manufacturing process.